Embodiments of the present invention relate to apparatus and methods for computing filter coefficients for an adaptive filter for filtering a microphone signal so as to suppress an echo due to a loudspeaker signal, as may be employed, for example, within the context of conference systems. Examples of conference systems include telephone conference systems, video conference systems or other bi-directional conference systems.
Acoustic echoes arise whenever tones, sounds and noises from a loudspeaker are picked up by a microphone located in the same room or in the same acoustic environment. In telecommunication systems, this acoustic feedback signal is transmitted back to the far-end subscriber, who notices a delayed version of their own speech. In this context, echo signals represent a very distracting disturbance and may even inhibit interactive full-duplex communication. Additionally, acoustic echoes may result in howling effects and other instabilities of the acoustic feedback loop.
WO 2006/111370 A1 relates to a method and an apparatus for removing an echo in a multichannel audio signal. Acoustic echo control and noise suppression are an important part of any hands-free telecommunication system such as telephone, audio or video conference systems. The method, described in the document, of processing multichannel audio loudspeaker signals and at least one microphone signal in this context includes the steps of transforming the input microphone signal to input microphone short-time spectra, computing a combined loudspeaker signal short-time spectrum from the loudspeaker signals, computing a combined microphone signal short-time spectrum from the input microphone signal, estimating a magnitude spectrum or a power spectrum of the echo in the combined microphone signal short-time spectrum, computing a gain filter for magnitude modification of the input microphone short-time spectrum, applying the gain filter to at least one input microphone spectrum, and converting the filtered input microphone spectrum to the time domain.
Echo suppression and echo cancellation systems as are employed today and may also be referred to as echo removal systems in summary, frequently have the problem that they do not cope with different sound, tone, noise components, and echo components in an optimum manner despite the use of adaptive filters. If one component is predominant as compared to another, a non-optimum suppression of the echo of the loudspeaker signal may occur in the microphone signal of such a communication system, for example. On the other hand, in the case of a deviating composition of the components of the different sources, tonal artifacts may arise due to the utilization of an echo suppression or echo cancellation system, which tonal artifacts are also perceived as extremely annoying.
EP 1 429 315 A1 refers to a method and system for suppressing echoes and noise in environments under variable acoustic conditions as well as conditions of a large feedback proportion. The system for canceling echoes and noises in environments with variable acoustic conditions and high feedback, such as the interior of an automotive vehicle, permitting audible communication between the occupants, comprises one or several microphones for a speech signal and A/D, D/A converters, amplification and filtering means generating an electric signal reproduced as an acoustic signal by a speaker, and an echo canceller using the signal and an electric signal from the microphone integrating the feedback signal of the signal, another speech signal and noise seized by the microphone. The system is applied to eliminating the feedback, by providing an additional filtering of an electric output signal of the canceling device, after treatment of the signal, comprising a time variant filter that suppresses the residual acoustic echo not cancelled by the system and the noise seized by the microphones.
WO 2009/095161 A1 relates to an apparatus and a method for computing filter coefficients for echo suppression. The filter coefficients are intended to be used with an adaptive filter for filtering a microphone signal so as to suppress an echo due to a loudspeaker signal. The apparatus includes extraction means for extracting a stationary component signal or a non-stationary component signal from the loudspeaker signal or from a signal derived from the loudspeaker signal. The apparatus also comprises computing means for computing the filter coefficients for the adaptive filter on the basis of the extracted stationary component signal and the non-stationary component signal. The apparatus and method disclosed in WO 2009/095161 examine the far-end signal with respect to statistical properties of the component signal that constitute the loudspeaker signal.